Posted by daestrom on November 17, 2011, 9:50 pm
On 11/16/2011 18:32 PM, m II wrote:
Well I disagree with your disagree statement.
It isn't a question of how strong the steel is, it's a matter of how the
winding is placed.
In conventional DC generator, the windings are placed axially in slots
with insulation and wedging. This wedging fails at high speeds,
allowing the winding to spill out of the slot.
Also the turns at each end of the rotor where the wire exits one slot,
travels part way around the rotor and enters another slot is subject to
failure. In tiny machines, the wire is self-supported. In larger
units, the end turns are banded with insulation and steel wire to hold
them inward against the centrifugal forces. Spin it fast enough and
when that support fails, the end turns bow outward, contact the stator
iron and get destroyed.
Because the alternator winding is mounted in between the two iron rotor
pieces, and they each have about 14 steel teeth bent towards the
opposite piece, they provide a very strong case to hold the copper
windings inside. The 'teeth' are about 3/8 inch by 1/2 inch square
steel bar (or larger). When assembled, there is very little space
between them and the wire is crossing the gap at nearly right angles,
not lined along the gap like the slots in a DC generator. (The steel
pieces are forged and heat treated, not cast, BTW)
DC generators are also limited in speed by the commutator construction.
All the bars are held in place with just a couple of bands, one on
each end (on small machines, sometimes steel wire wrapped over the bars
with insulation). At high speeds these bands can stretch from the
extreme forces. This lets the bars slip in relation to one another.
Even if the bars don't come out completely from under the banding, once
a bar slips the brushes get chopped off by the high bar like a buzz-saw
in a matter of seconds.
These problems are also eliminated with an alternator and replaced with
single piece slip rings that are made of one piece (again, much stronger
Posted by m II on November 18, 2011, 12:11 am
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Well I disagree with your disagree with my disagree statement.
Not because you're wrong, but because I'm just contrary. Everything you
say is true, but you can't discount the difference in centrifugal force
between a field winding and a main current carrying one. The weight per
unit difference alone would be enough to let the alternator spin three
times as fast as a generator.
That's my story, and I'm sticking to it.
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Posted by Morris Dovey on November 14, 2011, 7:49 pm
On 11/14/11 12:28 PM, Rick wrote:
It was one of those things that was better in concept than in practice.
There are a couple of people who've managed to get their hands on these
things, and they all say the darned things have more value as souvenirs
than as generators.
I think we /can/ build much more efficient Stirling engines, but it'll
require some serious work to develop the technology. Most of the people
now involved are (re)inventing from what they can see in their rear-view
Posted by Morris Dovey on November 14, 2011, 7:35 pm
On 11/14/11 12:03 PM, Rick wrote:
Interesting, but it doesn't appear to be in the same price class as
Briggs & Stratton (et al). I've done a lot of searching, but it doesn't
appear that anyone is offering consumer-affordable products.
Still looking - and hoping (but not holding my breath).
Posted by harry k on November 14, 2011, 7:55 pm
Yep. The Stirling does have some hope of practical use. I will make
a prediction that if it ever does, it will be in a very limited
application. For sure beats out the wackos pushing "the Amazing Air
Car", the "Psuedoturbine" and the like :)